The present invention is directed to a viscous fluid coupling device for use in motor vehicles and more particularly to a viscous fluid coupling device for driving an engine cooling fan assembly. Many prior art viscous fluid coupling devices are comprised of a rotor fixed for rotation on an engine driven shaft and a fan carrying housing surrounding the rotor and journaled for rotation relative to the shaft. The interior of the housing is generally divided into a working chamber containing the rotor and a reservoir chamber by means of a partition plate having one or more passages therethrough which are controlled by a thermostatically operated valve plate.
An example of such a viscous fluid coupling is disclosed in U.S. Pat. No. 3,990,556 granted Nov. 9, 1976 to Hayashi et al. In this patent, the partition plate which defines the reservoir chamber and the working chamber is secured at the outer periphery thereof to an inside shoulder of the housing by means of swaging. In such a swaging operation, a portion of the metallic shoulder is rolled over the outer peripheral edge of the partition plate to secure the partition plate to the housing. Such a swaging operation requires special machinery and involves a very difficult and complicated operation within the narrow confines of the housing.